View Full Version : UL- what it means

T. Ashley McGrew
01-21-2011, 08:04 PM
If you work in a museum with a risk management officer or department then you are probably used to the requirement that electronic components be UL listed (UL for Underwriters Laboratories).
The following is an interesting response posted on another listserve. I enjoyed it, and now know what a "wall wort" is. With the authors permission here it is.
Thanks Maris

Date: Wed, 12 Jan 2011 08:01:06 -0800
From: Maris Ensing <maris@MADSYSTEMS.COM>
Subject: Re: "UL" what it means

UL is somewhat like CE in Europe. The main differences are that CE is there
to protect people and affects everything from battery operated devices to
toys to mains powered devices. In the case of mains powered devices tests
relate to making sure that people cannot touch anything hot or dangerous,
the capability of devices to survive power surges or externally induced
static, and the radio wave emission and susceptibility. UL relates to
devices that are connected to mains power, and is mainly designed to protect
equipment and facilities. UL testing involves making sure that power
connections are made propely, and that the correct materials are being used
to avoid fires in case something goes wrong.

UL is not applicable to equipment that is battery powered or low voltage
powered (ie. 12VDC or similar). When it comes to "UL" make sure equipment
says "UL Listed" rather than "UL compatible" or similar statements which
have no meaning. Unlike CE, UL listing is NOT a requirement in a lot of
cases, which is why non-UL equipment is available and perfectly legal -
although you would NOT expect to see it used in professional installations,
and very often in our world, clients insist that all equipment is UL listed
as it would affect their insurance (risk).

One reason why we see a lot of "wallwarts" here (external power supplies) is
that the power supply has to be UL listed, but that the low voltage output
(and therefore feed into the target equipment) makes the UL listing
irrelevant to the equipment itself - ie. A computer that you plug into mains
power (110VAC) should be UL listed. In the case of a laptop, the power
supply should be UL listed, but since the laptop is fed with 19V or similar,
it does not require a UL listing.